I must admit, I know absolutely nothing about colours, apart from the way that they are bloody hard to get to work together.
I had a revelation today when I asked one of the graphic designers to give me a colour that matched the rest of the site, she pulled out a pantone swatch and told me the value I needed. Incredible! I'd never seen a pantone thing before, I thought they did it all by eye.
Anyway the colour scale goes: Red -> brown -> yellow -> green -> blue (blue is 50 knots or so

) It's a continuous scale and I think it's sort of logarithmic. Anyway watch it for a couple of weeks and you'll figure out how it works. It might need a bit of tweaking I think, the arrows are a bit greener than I think they should be for a certain strength wind.
The wind data is taken from Weatherzone here:
www.weatherzone.com.au/services/rss.jsp so I think it's taking readings from each city's airport.